The present invention relates to new catalyst systems and to their use in the oligomerization and co-oligomerization of (xcex1-olefins; said catalyst systems are particularly useful in ethylene oligomerization in order to obtain xcex1-olefinic oligomers having from 4 to 24 carbon atoms.
High linear xcex1-olefins, i.e. (xcex1-olefins having from 4 to 24 carbon atoms, and more specifically 6 to 20 carbon atoms, are in great demand as intermediates in the preparation of detergents, lubricant additives and polyolefins; xcex1-olefins having 6-20 carbon atoms are suitable for a large number of applications in different technical fields. However, oligomerization processes commonly known in the state of the art lead to the obtainment, together with the target products, of undesirable by-products, such as internal olefins, branched olefins and olefins having a number of carbon atoms outside the above mentioned range.
Olefin polymerization processes employing homogeneous Ziegler-Natta catalyst systems or metallocene/alumoxane catalyst systems are well known in the state of the art; these catalyst systems are also used in oligomerization processes of lower olefins to give higher olefins.
For instance, the British patent application GB 135,873 describes the preparation of C4-C20 linear xcex1-olefins by ethylene oligomerization in the presence of a catalyst composition comprising a divalent nickel salt, a boron hydride and a tertiary organophosphorus compound.
The international patent application WO 94/25416 discloses a catalyst system for the preparation of C4-C24 linear xcex1-olefins comprising the reaction product of a bis-tetramethyl-cyclopentadienyl metallocene and a bulky, labile and non-coordinating anion.
Bridged bis-amido Group 4 (IUPAC 1988 notation) metal compounds are also known, as components of catalyst systems for the preparation of polyolefins, such as polyethylene and polypropylene. The international patent application WO 92/12162 discloses catalyst systems for the polymerization of xcex1-olefins, comprising an amido transition metal compound having the following formula: 
wherein M is Ti, Zr or Hf; X is an univalent anionic ligand; the groups R, linked to trivalent N atoms, are selected from halogens and linear or branched hydrocarbon radicals, optionally containing one or more heteroatoms; T is a covalent unsubstituted or substituted hydrocarbon bridging group, optionally containing one element of Group IV-A or VI-A (Deming notation; corresponding to Group 14 and 16 of the IUPAC 1988 notation); y is 1 or 0; z is 2-y;
in association with an alumoxane.
Suitable alumoxanes are obtained by hydrolysis of a trialkylaluminium or haloalkylaluminium, such as trimethylaluminium, triethylaluminium and the corresponding chlorides; the most preferred alumoxane is methylalumoxane (MAO).
The catalysts disclosed in the above-mentioned WO 92/12162, which do not envisage amido compounds having a bridging group containing two heteroatoms, are used in the production of high molecular weight polyolefins, having a molecular weight well in excess of 100,000, and more specifically of high molecular weight isotactic polypropylene.
The international patent application WO 96/27439 describes a new class of oligomerization catalysts comprising a bridged bis-amido Group 4 metal compound, such as {1,2-bis(t-butylamide)tetramethyl-disilane{-zirconium dibenzyl or dimethyl, in association with suitable activating agents, capable of providing a bulky, labile and non-coordinating anion, containing at least one boron atom, such as B(C6F5)3 or [Me2PhNH]+[B(C6F5)4]xe2x88x92.
These catalyst systems are active in the oligomerization or co-oligomerization of xcex1-olefins to produce linear xcex1-olefins. In the specification of WO 96/27439 it is mentioned the possibility of adding to the catalytic compositions further components, for example in order to increase the solubility and/or the stability of the same compositions, although not affecting the catalytic activity. For instance, it is mentioned the possibility of adding organoaluminium compounds, such as trimethylaluminium (TMA), triethylaluminium (TEA), triisopropylaluminium and triisobutylaluminium (TIBA), acting as scavenging agents, although without any influence of the catalytic activity of the system.
Nevertheless, there is room for improvement in the oligomerization yields when these catalyst systems are used. They tend to be sensitive to the presence of minor contaminants, resulting in low yields. In order to achieve a satisfactory activity the catalyst concentrations should not be too low, whereas relatively high concentrations may lead to exothermic reactions which are difficult to control. Further, the activity stability of the catalyst systems described in WO 96/27439 is not optimal, as shown by their activity decay.
Therefore, it is felt the need of lowering the decay rate and improving the catalytic activity of the above mentioned oligomerization catalysts, in order to allow their industrial exploitation.
The Applicant has now unexpectedly found that the catalytic activity in xcex1-olefin oligomerization of the above-mentioned bridged bis-amido Group 4 metal compounds, in association with boron activating compounds, can be surprisingly enhanced by adding to these components a specific class of branched alkylaluminiums and/or alumoxanes of branched alkylaluminiums, leading to xcex1-olefin oligomers having from 4 to 30 carbon atoms, in high yields and with a high selectivity towards xcex1-olefins.
More specifically, the present invention concerns a catalyst system for xcex1-olefin oligomerization comprising the product obtainable by contacting the following components:
(A) one or more bis-amido compounds having formula (I): 
wherein M is Ti, Zr or Hf;
N is a trivalent nitrogen atom;
the Y atoms, the same or different from each other, are selected from the group consisting of Si, Ge and Sn;
the X groups, the same or different from each other, are selected from the group consisting of H, halogen, linear or branched, saturated or unsaturated C1-C20 alkyl, C1-C20 alkoxyl, C3-C20 cycloalkyl, C6-C20 aryl, C6-C20 aryloxyl, C7-C20 alkylaryl and C7-C20 arylalkyl radicals, optionally containing one or more Si, Ge, O, S, P, B or N atoms; or two X groups form a ring having from 4 to 8 members;
R1, R2, R3, R4, R5 and R6, the same or different from each other, are linear or branched, saturated or unsaturated C1-C20 alkyl, C3-C20 cycloalkyl, C6-C20 aryl, C7-C20 alkylaryl or C7-C20 arylalkyl radicals, optionally containing one or more Si, Ge, O, S, P, B or N atoms; or are Si(R7)3 groups, wherein the groups R7, the same or different from each other, are linear or branched, saturated or unsaturated C1-C10 alkyl, C3-C10 cycloalkyl, C6-C15 aryl, C7-C15 alkylaryl or C7-C15 arylalkyl groups; or two or four substituents of R1, R2, R3, R4, R5 and R6, linked to two vicinal atoms, form one or two rings having from 4 to 8 members;
Q is a neutral Lewis base; and
m is an integer ranging from 0 to 2;
said bis-amido compound being optionally present in the form of a dimer;
(B) one or more activating cocatalysts selected from:
compounds having formula Y+Zxe2x88x92, wherein Y+ is a cation capable of reacting irreversibly with a substituent X of the compound of formula (I), and Zxe2x88x92is a compatible non-coordinating anion comprising at least one boron atom; and
neutral strongly Lewis acidic compounds comprising at least one boron atom;
(C) one or more compounds selected from the following classes:
(a) organometallic aluminium compounds having formula (II):
Al(CH2xe2x80x94CR8R9R10)xR11yHzxe2x80x83xe2x80x83(II)
wherein, in the (CH2xe2x80x94CR8R9R10) groups, the same or different from each other, R8 is a linear or branched, saturated or unsaturated C1-C10 alkyl, C3-C13 cycloalkyl or C7-C16 alkylaryl radical; R9 is a saturated or unsaturated C1-C50 alkyl, C3-C50 cycloalkyl, C6-C50 aryl, C7-C50, alkylaryl or C7-C50 arylalkyl radical, said radical being different from a straight alkyl or alkenyl group; or R8 and R9 form together a ring having from 4 to 6 carbon atoms; R10 is hydrogen or a linear or branched, saturated or unsaturated C1-C10 alkyl, C6-C15 aryl, C7-C16 alkylaryl radical or arylalkyl radical, optionally containing one or more Si or Ge atoms;
R11 is a linear or branched, saturated or unsaturated C1-C10 alkyl, C3-C15 cycloalkyl, C6-C15 aryl, C7-C16 alkylaryl or C7-C16 arylalkyl radical;
x is an integer ranging from 1 to 3; z is 0 or 1; and y is 3-x-z; and
(b) the reaction products of water with organometallic aluminium compounds of formula (III):
AlR123xe2x88x92wHwxe2x80x83xe2x80x83(III)
wherein the substituents R12, the same or different from each other, are selected from the group consisting of linear or branched, saturated or unsaturated C1-C50 alkyl, C3-C50 cycloalkyl, C6-C50 aryl, C7-C50 alkylaryl and C7-C50 arylalkyl radicals, optionally containing one or more Si or Ge atoms, wherein at least one of said substituents R12 is different from a straight alkyl group; and w is 0 or 1; the molar ratio between said organometallic aluminium compound and water being comprised between 1:1 and 100:1.
The present invention further provides a process for the oligomerization of olefins comprising the reaction of oligomerization of one or more olefinic monomers in the presence of a catalyst system as reported above.
The catalyst systems for olefin oligomerization and the process using them, according to the present invention, will be better described in the following detailed description.
In the bis-amido compounds (A) having formula (I), M is Ti, Zr or Hf, and preferably is Zr. The groups Y are preferably the same, and are more preferably two Si atoms.
The groups X are preferably selected from hydrogen, methyl, ethyl, propyl, n-butyl, phenyl, 4-alkyl-phenyl and benzyl groups; two X groups can form, together with the metal M, a ring having from 4 to 8 members, and preferably a metallacyclobutane.
R1, R2, R3, R4, R5 and R6, the same or different from each other, are preferably methyl, ethyl, propyl, n-butyl, t-butyl, t-amyl, cyclohexyl, phenyl, dimethyl-phenyl, diisopropyl-phenyl, trimethylsilyl, tri-t-butyl-silyl, phenylmethyl-ethyl, diphenyl-ethyl and triphenyl-methyl.
Preferred examples of the neutral Lewis base Q are diethylether, tetrahydrofuran, dimethylaniline, aniline, n-butylamine and trimethylphosphine.
Preferred bis-amido compounds of formula (I) according to the present invention are:
{1,2-bis(t-butylamide)-tetramethyldisilane}metal dibenzyl {(Me2SiNCMe3)2}M(CH2Ph)2 
{1,2-bis(t-butylamide)-tetramethyldisilane}metal dimethyl, {(Me2SiNCMe3)2}MMe2 
{1,2-bis(t-butylamide)-tetramethyldisilane}metal di(n-butyl), {(Me2SiNCMe3)2}M(n-Bu)2 
{1,2-bis(t-butylamide)-tetramethyldisilane}metal diphenyl, {(Me2SiNCMe3)2}MPh2 
{1,2-bis(t-butylamide)-tetramethyldisilane}metal di(4-methylphenyl), {(Me2SiNCMe3)2}M {CH2(4-Me-Ph)}2 
{1,2-bis(t-butylamide)-tetramethyldisilane}metallacyclobutane, {(Me2SiNCMe3)2}{MCH2CH2CH2}
{1,2-bis(t-butylamide)-tetramethyldisilane}metal dihydride, {(Me2SiNCMe3)2}MH2 
{1,2-bis(t-amylamide)-tetramethyldisilane}metal dibenzyl, {(Me2SiNCMe2Et)2}M(CH2Ph)2 
{1,2-bis(cyclohexylamide)-tetramethyldisilane}metal dibenzyl, {(Me2SiNCy)2}M(CH2Ph)2 
{1,2-bis(ethylamide)-tetramethyldisilane}metal dibenzyl, {(Me2SiNEt)2}M(CH2Ph)2 
{1,2-bis(phenylamide)-tetramethyldisilane }metal dibenzyl, {(Me2SiNPh)2}M(CH2Ph)2 
{1,2-bis(2,6-dimethylphenylamide)-tetramethyldisilane}metal dibenzyl, {(Me2SiN[2,6-Me2-Ph])2}M(CH2Ph)2 
{1 ,2-bis(trimethylsilylamide)-tetramethyldisilane}metal dibenzyl, {(Me2SiNSiMe3)2}M(CH2Ph)2 
{1,2-bis{tri(t-butyl)silylamide)-tetramethyldisilane}metal dibenzyl, [{(Me2SiNSi(CMe3)3}2]M(CH2Ph)2 
{1,2-bis(t-butylamide)-tetraethyldisilane}metal dibenzyl, {(Et2SiNCMe3)2}M(CH2Ph)2 
{1,2-bis(t-butylamide)-tetraethyldisilane}metal dimethyl, {(Et2SiNCMe3)2}MMe2 
{1,2-bis(t-butylamide)-tetraphenyldisilane }metal dibenzyl, {(Ph2SiNCMe3)2}M(CH2Ph)2 
{1,2-bis(t-butylamide)-tetramethyldigermane}metal dibenzyl, {(Me2GeNCMe3)2}M(CH2Ph)2 
{1,2-bis(t-butylamide)-tetramethyldistannane}metal dibenzyl, {(Me2SnNCMe3)2}M(CH2ph)2,
{1,2-bis( 1,1,3,3-tetramethylbutylamide)-tetramethyldisilane}metal dibenzyl, {(Me2SiNCMe2CH2CMe3)2}M(CH2Ph)2, and
{1,2-bis(2,6-diisopropylphenylamide)-tetramethyldisilane}metal dibenzyl, {(Me2SiN[2,6-iPr2Ph])2}M(CH2Ph)2,
wherein M has the meaning reported above.
The bis-amido Group 4 metal compounds of formula (I), i.e. components (A) of the catalyst systems of the invention, can be prepared according to procedures known in the state of the art, and more specifically as described in the international patent application WO 96/27439. Said bis-amido compounds can be in the form of a dimer, corresponding to the following formula (IV): 
wherein M, Y, X, R1, R2, R3, R4, R5, R6 and Q have the meaning reported above and n is 0 or 1.
The catalyst systems of the invention further comprise one or more activating cocatalysts (component B) of formula Y+Zxe2x88x92, wherein Yxe2x88x92 is a cation capable of reacting irreversibly with a substituent X of the compound of formula (I) or (IV), and Zxe2x88x92 is a bulky and labile anion, substantially non-coordinating under the reaction conditions, and containing at least one boron atom. Further suitable activating cocatalysts are neutral Lewis acidic compounds, containing at least one boron atom, which are capable of abstracting one of the radicals X of the first component, thereby also contributing an anion Zxe2x88x92. Said anion must be capable of stabilizing the active catalytic species originating by the reaction of the compound (I) or (IV) with said activating cocatalyst and must be sufficiently labile to be able to be displaced by an olefinic substrate.
Components (A) and (B) form together an ionic compound of formula (V): 
wherein M, Y, X, R1, R2, R3, R4, R5, R6, Q, Z and m have the meaning reported above; or, when the component (A) is in the form of the above reported dimer (IV), an ionic compound of formula (VI): 
wherein M, Y, X, R1, R2, R3, R4, R5, R6, Q, Z and n have the meaning reported above. In component (B), Y+ is preferably a Broensted acid, capable of donating a proton and of reacting irreversibly with a substituent X of the compound of formula (I) or (IV); the cation Y+ is preferably a quaternary ammonium cation, and more preferably a trihydrocarbyl-ammonium cation, such as tri-n-butylammonium and dimethylanilinium.
Alternatively Y+ is a not proton-donating cation, in particular a metal cation, such as a silver ion or a triphenyl carbenium ion.
In component (B), the anion Zxe2x88x92, containing one boron atom, is preferably a borate of formula [B(RI)4]xe2x88x92, wherein R1 is selected from the group consisting of hydrogen, C1-C10 alkyl, C3-C10 cycloalkyl, C6-C15 aryl, C7-C15 alkylaryl and C7-C15 arylalkyl groups, optionally substituted with one or more halogens; suitable examples are [B(C6F5)4]xe2x88x92, [RIB(C6F5)3]xe2x88x92, [B(FC6H4)4]xe2x88x92, [RIB(FC6H4)3]xe2x88x92, [B{(CF3)2(C6H3)}4]xe2x88x92 and [RIB{(CF3)2(C6H3)}3]xe2x88x92, wherein RI has the meaning reported above. Examples of anion Zxe2x88x92 containing a plurality of boron atoms are the carborates, such as [B11CH12]xe2x88x92.
The activating cocatalyst Y+Zxe2x88x92 is preferably selected from the group consisting of:
dimethylanilinium tetrakis(pentafluorophenyl)borate [PhMe2NH][B(C6F5)4],
tri(n-butyl)ammonium tetrakis(pentafluorophenyl)borate [Bu3NH][B(C6F5)4],
dimethylanilinium tetrakis(2,3,5,6-tetrafluorophenyl)borate [PhMe2NH][B(2,3,5,6xe2x80x94C6F4H)4],
dimethylanilinium tetrakis(3,5-bis-trifluoromethyl-phenyl)borate [PhMe2NH][B(3,5-(CF3)2xe2x80x94C6H3)4],
dimethylanilinium tetrakis(4-fluorophenyl)borate [PhMe2NH][B(4-C6H4F)4],
dimethylanilinium tetraphenylborate [PhMe2NH][B(C6H5)4],
triphenylcarbonium tetrakis(pentafluorophenyl)borate [Ph3C][B(C6F5)4],
ferrocenium tetrakis(pentafluorophenyl)borate [(C5H5)2Fe][B(C6F5)4],
silver tetrakis(pentafluorophenyl)borate [Ag][B(C6F5)4],
tri(n-butyl)ammonium 1-carbodecaborate [Bu3NH][CB11H12] and
diethyloxonium tetrakis(3,5-bis-trifluoromethyl-phenyl)borate [H(OEt2)2][B(3,5-(CF3)2xe2x80x94C6H3)4].
When component (B) is a neutral strongly Lewis acidic compound, it is preferably selected from the group consisting of:
tris(pentafluorophenyl)borane B(C6F5)3,
tris(2,3,5,6-tetrafluorophenyl)borane B(2,3,5,6-C6F4H)3, and
trimethylboron B(CH3)3.
The boron containing components (B) of the catalyst systems of the invention can be prepared according to procedures known in the state of the art, and in particular as described in the international patent application WO 96/27439.
Component (C) of the catalyst systems according to the present invention can be one or more organometallic aluminium compounds belonging to the following classes:
(a) organometallic aluminium compounds of formula (II):
Al(CH2xe2x80x94CR8R9R10)xR11yHzxe2x80x83xe2x80x83(11)
wherein R8, R9, R10, R11, x, y and z have the meaning reported above; and
(b) reaction products of water with organometallic aluminium compounds of formula (III)
AlR123xe2x88x92wHwxe2x80x83xe2x80x83(III)
wherein R12 and w have the meaning reported above.
In the organometallic aluminium compound belongs to the class (a), formula (II), R8is preferably methyl or ethyl; R9 is preferably a saturated or unsaturated branched-chain C3-C30 alkyl or alkylaryl group, and more preferably a C4-C10 alkyl or alkylaryl group, or it is an optionally substituted phenyl group; R10 is preferably hydrogen; R11 is preferably a C1-C5 alkyl group, and more preferably an isobutyl group.
The above organometallic aluminium compounds can be suitably prepared according to the methods known in the state of the art, and preferably as described in the international patent application WO 96/02580.
A subclass of organometallic aluminium compounds particularly advantageous in the catalyst systems according to the present invention are the compounds of formula (II) wherein the (CH2xe2x80x94CR8R9R10) groups, the same or different from each other, are xcex2,xcex4-branched groups, corresponding to formula (CH2xe2x80x94CR8R10xe2x80x94CH2xe2x80x94CR13R14R15), wherein R8 and R10 have the meaning reported above; R13 and R14, the same or different from each other, are linear or branched, saturated or unsaturated C1-C20 alkyl, C3-C20 cycloalkyl, C6-C20 aryl, C7-C20 alkylaryl and C7-C20 arylalkyl radicals; and R15 is hydrogen or has the same meaning of R13 and R14. Non limiting examples of these compounds are tris(2,4,4-trimethylpentyl)aluminium (TIOA), bis(2,4,4-trimethylpentyl)aluminium hydride, isobutyl-bis(2,4,4-trimethylpentyl)aluminium, diisobutyl-(2,4,4-trimethylpentyl)aluminium, tris(2,4-dimethylheptyl)aluminium and bis(2,4-dimethylheptyl)aluminium hydride.
Another particular class of organometallic aluminium compounds of formula (II), suitable as a component (C) of the catalyst systems of the invention, are those wherein the (CH2xe2x80x94CR8R9R10) groups derive from the product of the oligomerization of lower xcex1-olefins, such as propylene or 1-butene. In this case, x is preferably 1 or 2.
These compounds can be prepared as described in the above-mentioned international patent application WO 96/02580.
A particularly preferred subclass of organometallic aluminium compounds is constituted by the compounds of formula (II) wherein the (CH2xe2x80x94CR8R9R10) groups, the same or different from each other, are xcex2,xcex3-branched groups, corresponding to formula (CH2xe2x80x94CR8R10xe2x80x94CR13R14R15), wherein R8, R10, R13, R14 and R15 have the meaning reported above. In said subclass, R8 is preferably a C1-C5, more preferably a C1-C3 alkyl group; according to a preferred embodiment, said R8 is methyl. R10 is preferably hydrogen. R13 and R14 are preferably C1-C5, and more preferably C1-C3 alkyl groups. R15 is preferably hydrogen or a C1-C5 alkyl group, and more preferably a C1-C3 alkyl group.
Within this subclass, particularly preferred organometallic aluminium compounds are: tris(2,3-dimethyl-butyl)aluminium, tris(2,3,3-trimethyl-butyl)aluminium, tris(2,3-dimethyl-pentyl)aluminium, tris(2,3-dimethyl-hexyl)aluminium, tris(2,3-dimethyl-heptyl)aluminium, tris(2-methyl-3-ethyl-pentyl)aluminium, tris(2-methyl-3-ethyl-hexyl)aluminium, tris(2-methyl-3-ethyl-heptyl)aluminium, tris(2-methyl-3-propyl-hexyl)aluminium, tris(2-ethyl-3-methyl-butyl)aluminium, tris(2-ethyl-3-methyl-pentyl)aluminium, tris(2,3-diethyl-pentyl)aluminium, tris(2-propyl-3-methyl-butyl)aluminium, tris(2-isopropyl-3-methyl-butyl)aluminium, tris(2-isobutyl-3-methyl-pentyl)aluminium, tris(2,3,3-trimethyl-pentyl)aluminium, tris(2,3,3-trimethyl-hexyl)aluminium, tris(2-ethyl-3,3-dimethyl-butyl)aluminium, tris(2-ethyl-3,3-dimethyl-pentyl)aluminium, tris(2-isopropyl-3,3-dimethyl-butyl)aluminium, tris(2-trimethylsilyl-propyl)aluminium, tris(2-methyl-3-phenyl-butyl)aluminium, tris(2-ethyl-3-phenyl-butyl)aluminium, tris(2,3-dimethyl-3-phenyl-butyl)aluminium, and the corresponding compounds wherein one of the hydrocarbyl groups is replaced by hydrogen, and those wherein one or two of the hydrocarbyl groups are replaced by an isobutyl group.
These organoaluminium compounds can be prepared according to procedures known in the state of the art, and in particular as described in the International Application no. PCT/EP 98/06732.
When component (C) of the catalyst systems according to the present invention belongs to class (b), it is the reaction product of water with an organometallic aluminium compounds of formula (III), as reported above. The molar ratio between said organometallic aluminium compound and water ranges from 1:1 to 100:1, and preferably from 1:1 to 50:1. A particularly advantageous value of said molar ratio is 2:1.
In formula (III), R12 is preferably a substituted or unsubstituted non-straight C1-C10 alkyl or C7-C16 alkylaryl, optionally containing Si or Ge atoms; more preferably, all the substituents R12 are isoalkyl radicals.
The compounds of formula (III) are preferably selected from the group consisting of Al(iBu)3 (TIBA), AlH(iBu)2, Al(iHex)3, Al(C6H5)3, Al(CH2C6H5)3, Al(CH2CMe3)3, Al(CH2SiMe3)3, AlMe2iBu and AlMe(iBu)2.
According to a further preferred embodiment of the catalyst system of the invention, said organometallic aluminium compounds of formula (III) corresponds to the compounds of formula (II), as reported above, and the preferred compounds are the above-mentioned ones.
According to a further preferred embodiment of the invention, in said compound of formula (III), at least one R12 group has formula (CH2xe2x80x94CR8R9R10), wherein R8, R9 and R10 have the meaning reported above; more preferably said R12 group is a xcex2,xcex4-branched or a xcex2,xcex3-branched group.
When component (C) belong to class (b), water can be gradually added to the alkyl aluminium compound of formula (III) in solution, in an aliphatic or aromatic inert hydrocarbon solvent such as heptane or toluene; preferably, compound (C) of formula (III) can be brought into contact with the wet monomer or solvent in the reactor and the mixture of components (A) and (B) and an additional amount of compound (C) is then introduced into the reactor.
According to another embodiment, water can be reacted in combined form as hydrated salt, or it can be absorbed or adsorbed on an inert support, such as silica. According to a further embodiment, the alkyl aluminium compound (III) can be allowed to react with boric anhydride or with boric acid.
The components of the catalyst system according to the present invention can be brought into contact in different manners. The catalyst system may be formed by mixing together components (A), (B) and (C), following different orders of addition, preferably in solution, in a suitable non-polar solvent such as toluene, benzene, chlorobenzene, an alkane or an alkene, to form a liquid catalyst system. A preferred way of forming the catalyst system of the invention comprises first mixing components (A) and (B), and subsequently adding to the obtained mixture a solution of component (C), preferably in toluene.
The three-components catalyst system may be formed prior to its introduction into the reaction vessel, or it may be formed in situ.
Components (A) and (B) are preferably employed with a molar ratio ranging from 0.1:1 to 5:1, and more preferably ranging from 0.9:1 to 1.1:1.
The molar ratio between the aluminium of component (C) and the metal M of the bis-amido compound (A) preferably ranges from 1:1 to 1000:1, more preferably from 10.1 to 500:1, and even more preferably from 20:1 to 150:1.
The catalysts of the present invention can also be used on inert supports. This is achieved by depositing the components (A), (B) and/or (C), either singly or in mixture, on inert supports such as silica, alumina, silica/alumina, titania, zirconia, magnesia; suitable inert supports are olefin polymers or prepolymers, such as polyethylenes, polypropylenes or styrene/divinylbenzene copolymers. The thus obtained supported catalyst systems can be advantageously used in gas-phase oligomerization.
The catalyst systems according to the present invention can be conveniently used in oligomerization processes. In fact, the Applicant has surprisingly found that the presence of the component (C) in the catalyst system according to the present invention leads to higher oligomerization yields, lower decay rates and better reproducibility, as well as to a better specificity in the obtainment of xcex1-olefins, thus avoiding the undesired formation of internal or branched olefins. Therefore, it is another object of the present invention a process for the oligomerization or co-oligomerization of a-olefins of formula CH2xe2x95x90CHR, wherein R is hydrogen or a C1-C20 alkyl, C5-C20 cycloalkyl or C6-C20 aryl radical, and preferably ethylene, in order to obtain linear xcex1-olefinic oligomers having a chain length from 4 to 30 carbon atoms and preferably 6-20 carbon atoms; said process is characterized in that the oligomerization reaction is performed in the presence of a catalyst system according to the present invention.
Non limiting examples of olefinic monomers which are suitable to be used in the oligomerization process according to the present invention are ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 4,6-dimethyl-1-heptene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene and allylcyclohexane, as well as cycloolefins (such as cyclopentene and cyclohexene) and conjugated or non-conjugated dienes (such as 1,4-hexadiene, isoprene, 1,3-butadiene, 1,5-hexadiene and 1,6-heptadienes).
The (co)oligomerization process according to the present invention can be carried out in the liquid phase or in gas phase; in the former case, it is advantageously carried out in the presence of an inert hydrocarbon solvent either aromatic, preferably toluene, or aliphatic, such as propane, hexane, heptane, isobutane, isopentane, cyclohexane and isooctane, and preferably isopentane or isooctane. Said solvent can serve even as a suitable solvent for the catalyst system.
Alternatively, the (co)oligomerization process may be carried out in an olefin solvent, and particularly in a mixture of linear xcex1-olefins and/or higher branched or internal olefins.
The starting xcex1-olefins can be supplied to the reactor together with an inert diluent, such as nitrogen or helium, when the reactant is gaseous, or in a liquid solvent when the reactant is in the liquid form.
The (co)oligomerization temperature is preferably comprised between xe2x88x9220xc2x0 C. and 150xc2x0 C., more preferably between 10xc2x0 C. and 100xc2x0 C., and even more preferably between 40 and 90xc2x0 C.
The (co)oligomerization pressure is preferably comprised between 100 and 10,000 kPa, more preferably between 200 and 8,000 kPa, and even more preferably between 500 and 2,000 kPa.
Reaction times of from 1 minute to 5 hours have been found to be suitable, depending on the activity of the catalyst system and on the reaction conditions. At the end of the oligomerization reaction, a conventional catalyst deactivating agent, such as water, methanol, or another alcohol, may be added to the reaction mixture, in order to terminate the reaction The reaction can be terminated also by introducing air.
Suitable operating conditions, in particular pressure and temperature, can be selected in order to yield oligomers having a xe2x80x9cK factorxe2x80x9d ranging from 0.3 to 0.8, wherein said xe2x80x9cK factorxe2x80x9d is the molar ratio [Cn+2]/[Cn], calculated from the slope of the graph of log [Cnmol %] versus n, wherein n is the number of carbon atoms in the olefinic product. The xe2x80x9cK factorxe2x80x9d gives an indication of the relative proportions of the olefins obtained from the oligomerization process.
The oligomerization product is a mixture of xcex1-olefins, preferably linear, having a chain length ranging from 4 to 30 carbon atoms, and preferably from 6 to 20 carbon atoms. Said olefins can be suitably recovered by conventional distillation and separation techniques, known in the state of the art. It is also possible to recover unconverted starting material and/or oligomeric products having a molecular weight outside the desired molecular weight, in order to process or recycle them.